People walk in a damaged area about a block away from the site of a Friday-evening gas explosion that leveled a strip club in Springfield, Mass. / Jessica Hill, AP

by USA TODAY

by USA TODAY

SPRINGFIELD, Mass. (AP) - A natural gas explosion that injured more than 20 people and damaged 42 buildings in Springfield's entertainment district was blamed on a utility worker who accidentally punctured a high-pressure pipeline while looking for a leak. The president of the gas company involved says the employee followed proper procedure and protocol.

State Fire Marshal Stephen Coan on Sunday said the Friday night blast in one of New England's largest cities was caused by "human error." He didn't name the Columbia Gas Co. worker who pierced the pipe while responding to reports of a gas leak.

The worker damaged the underground pipe while using a metal tool to locate the source of the leak, Coan said. A flood of gas then built up in a building that housed a strip club, and some kind of spark touched off the blast, officials said.

Coan said the employee was following older markings on a sidewalk that indicated the location of the gas line. He appeared to be an appropriate distance from the line, but the markings were incorrect and the worker accidentally punctured the pipe.

Columbia's president said the employee followed the correct procedures.

"You drive the hole to determine if there is any gas outside," Steve Bryant said. "He stepped over two feet and it turned out to be exactly the amount that the service was offset from the valve, which is a very unusual circumstance."

Bryant said the employee had the presence of mind to order an "appropriate" evacuation of the building.

Columbia, a subsidiary of public company NiSource Inc., plans to open a claims center at City Hall on Monday for residents and businesses affected by the explosion.

Preliminary reports show the blast damaged 42 buildings housing 115 residential units. Three buildings were immediately condemned, and 24 others require additional inspections by structural engineers to determine whether they are safe. The building that housed the Scores Gentleman's Club was destroyed.

After the pipe was ruptured, authorities evacuated several buildings. Most of the people injured were part of a group of gas workers, firefighters and police officers who ducked for cover behind a utility truck just before the blast. The truck was demolished.

Some officials said it was a miracle no one was killed. Springfield Fire Commissioner Joseph Conant praised the actions of city firefighters.

"The firefighters did an excellent job evacuating the area which certainly prevented additional civilian injuries and saved many lives," Conant said.

Columbia officials have been cooperating with investigators and have determined that there are no more gas leaks in the neighborhood, Mayor Domenic Sarno said.

Coan said the investigation is being turning over to the state Department of Public Utilities. It's not clear whether investigators will ever be able to determine what caused the spark that ignited the explosion.

Springfield, which is 90 miles west of Boston and has about 150,000 residents, is the largest city in western Massachusetts. It's known as the home of the Basketball Hall of Fame, which is not near the blast site.

The city has been rebuilding from damage caused by a tornado in June 2011.

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